Institute of Electrical and Electronics Engineers (IEEE) 802.11 is a set of physical and media access control (MAC) specifications for implementing wireless local area network (WLAN) communications. These specifications provide the basis for wireless network products using the Wi-Fi brand managed and defined by the Wi-Fi Alliance. The specifications define the use of the 2.400-2.500 GHz as well as the 4.915-5.825 GHz bands. These spectrum bands are commonly referred to as the 2.4 GHz and 5 GHz bands. Each spectrum is subdivided into channels with a center frequency and bandwidth. The 2.4 GHz band is divided into 14 channels spaced 5 MHz apart, though some countries regulate the availability of these channels. The 5 GHz band is more heavily regulated than the 2.4 GHz band and the spacing of channels varies across the spectrum with a minimum of a 5 MHz spacing dependent on the regulations of the respective country or territory.
WLAN devices are currently being deployed in diverse environments. These environment are characterized by the existence of many Access Points (APs) and non-AP stations (STAs) in geographically limited areas. Increased interference from neighboring devices gives rise to performance degradation. Additionally, WLAN devices are increasingly required to support a variety of applications such as video, cloud access, and offloading. Video traffic, in particular, is expected to be the dominant type of traffic in WLAN deployments. With the real-time requirements of some of these applications, WLAN users demand improved performance.
The IEEE 80211ax task group is discussing a High Efficiency WLAN (HEW) system that operates in the 2.4 GHz and 5 GHz bands and supports a channel bandwidth (or channel width) of 20 MHz, 40 MHz, 80 MHz, or 160 MHz. The HEW aims at improving performance felt by users demanding high-capacity and high-rate services. The HEW may support Orthogonal Frequency-Division Multiple Access (OFDMA) and thus may include the capability to handle multiple simultaneous transmissions (e.g., multi-user simultaneous transmission) in both the spatial and frequency domains, in both the uplink (UL) and downlink (DL) directions.
Link adaptation is a technique for adapting parameters of a wireless communications link between a transmitting STA and a receiving STA based on measurements of the link quality in order to maximize transmission rate. The receiving STA may provide feedback regarding the quality of the link to the transmitting STA. The transmitting STA may use this information to select an appropriate Modulation and Coding Scheme (MCS) to use when transmitting frames to the receiving STA.
Link adaptation feedback values for existing IEEE 802.11 systems are transmitted as part of the Media Access Control (MAC) header. However, link adaptation feedback in existing IEEE 802.11 systems only provide feedback for a given operation bandwidth (either 20 MHz, 40 MHz, 80 MHz, or 160 MHz). Also, existing IEEE 802.11 systems do not provide a way to transmit link adaptation feedback for users of a multi-user simultaneous transmission in a multi-user acknowledgment (ACK) frame.